Before transplanting your tomato plant seedlings outside, make your planting hole a bit deeper than usual, and drop 2 teaspoons of epsom salts in each planting hole. Sprinkle some dirt in the hole, and then add your seedling.
I also use epsom salts sprinkled around my rose bushes in the early spring before the rains come. It washes in and I don't know why it works, but my roses are lovely. I learned this from an old Mennonite farmer and his wife who were lovers till death and they had the most beautiful roses. He would sit out by a rose bush and wait for her to come sit in the sun with him each morning after the chores were done. They truly were a picture of love and both passed away the same year. Friends like this you never forget.